<!DOCTYPE html>
<html lang="zh-CN">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>演示页面</title>
    <script src="js/demo.js"></script>
    <!-- <script src="lib/jquery.min.js"></script> -->
    <!-- <link rel="stylesheet" href="lib/miniui/themes/default/miniui.css"> -->
    <!-- <script src="lib/miniui/miniui.js"></script> -->
    <link rel="stylesheet" href="css/style.css">
</head>

<body>
    <!-- <label for="js_send">
        结果：
    </label>
    <input type="text" id="js_send" name="js_send" style="font-size: 50px;">

    <div>
        <iframe id="inner" src="inner.html" frameborder="1" name="inner" title="inner"></iframe>
    </div> -->

    <div>
        <!-- <input type="text" name="whatever" title="whatever" class="plain-text" value="我长得像普通文本吗" readonly /> -->
        <!-- <br /> -->
        <textarea name="output" id="output"></textarea>
        <br />
        <button onclick="increment()">whatever</button>
    </div>

    <script>
        // document.getElementById("js_send").value = "imya";
        const output = document.getElementById("output");
        // let text = "";
        // function loopOutput(params) {
        //     for (let i = 0; i < 5; i++) {
        //         text += " " + i;
        //     }
        // }

        // loopOutput();
        let iSize = 0;
        function increment() {
            output.value = iSize;
            iSize++;
            if (iSize > 4) {
                iSize = 0;
            }
        }

        function judge() {
            let s;
            let s1 = null;
            if (s === s1) {
                output.value = 's为空字符串';
            }

            if (s === s1) {
                output.value = 's为null';
            }
        }

        judge();
    </script>
</body>

</html>